Heat spreading device and method

ABSTRACT

In an embodiment, a device includes: a die stack over and electrically connected to an interposer, the die stack including a topmost integrated circuit die including: a substrate having a front side and a back side opposite the front side, the front side of the substrate including an active surface; a dummy through substrate via (TSV) extending from the back side of the substrate at least partially into the substrate, the dummy TSV electrically isolated from the active surface; a thermal interface material over the topmost integrated circuit die; and a dummy connector in the thermal interface material, the thermal interface material surrounding the dummy connector, the dummy connector electrically isolated from the active surface of the topmost integrated circuit die.

PRIORITY CLAIM AND CROSS-REFERENCE

This application claims the benefit to U.S. Provisional PatentApplication No. 62/552,902, filed on Aug. 31, 2017, and entitled “HeatSpreading Device and Method,” which application is incorporated hereinby reference.

BACKGROUND

In the packaging of integrated circuits, semiconductor dies may bestacked through bonding, and may be bonded to other package componentssuch as interposers and package substrates. The resulting packages areknown as Three-Dimensional Integrated Circuits (3DICs). Heat dissipationis a challenge in the 3DICs.

A bottleneck may exist in efficiently dissipating the heat generated inthe inner dies of the 3DICs. In a typical 3DIC, the heat generated ininner dies may have to be dissipated to outer components before the heatcan be conducted to a heat spreader. Between the stacked dies and outercomponents, however, there exist other materials such as underfill,molding compound, and the like, which are not effective in conductingheat. As a result, the heat may be trapped in an inner region of abottom stacked die and cause a sharp local temperature peak (sometimesreferred to as a hot spot). Furthermore, hot spots due to heat generatedby high-power consuming dies may cause thermal crosstalk problems forsurrounding dies, negatively affecting the surrounding dies' performanceand the reliability of the whole 3DIC package.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a cross-sectional view of an integrated circuit die, inaccordance with some embodiments.

FIGS. 2A and 2B are cross-sectional views of die stacks, in accordancewith some embodiments.

FIGS. 3, 4, 5, 6, 7, 8A, 8B, 9, 10, 11, 12, 13, 14, and 15 are variousviews of intermediate steps during a process for forming a semiconductordevice, in accordance with some embodiments.

FIG. 16 shows the semiconductor device, in accordance with some otherembodiments.

FIG. 17 shows the semiconductor device, in accordance with some otherembodiments.

FIG. 18 shows the semiconductor device, in accordance with some otherembodiments.

FIG. 19 shows the semiconductor device, in accordance with some otherembodiments.

FIG. 20 shows the semiconductor device, in accordance with some otherembodiments.

FIG. 21 shows a dummy connector, in accordance with some otherembodiments.

FIG. 22 shows a flow diagram of a method for manufacturing asemiconductor device, in accordance with some other embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

In accordance with some embodiments, a die stack is formed on aninterposer and dummy vias are optionally formed in the die stack. Athermal interface material is formed over the die stack and dummyconnectors are formed in the thermal interface material. A heat spreaderis attached to the die stack with the thermal interface material.Forming the dummy vias and/or dummy connectors may reduce the thermalresistance along a thermal path between the interposer and heatspreader, thereby reducing operating temperatures of the resultingdevice.

FIG. 1 is a cross-sectional view of an integrated circuit die 50, inaccordance with some embodiments. The integrated circuit die 50 may bean interposer, logic device, or the like. The integrated circuit die 50includes a substrate 52, devices 54, conductive plugs 56, inter-layerdielectrics (ILDs) 58, an interconnect 60, die connectors 62, and adielectric material 64. The integrated circuit die 50 may be formed in awafer (not shown), which may include different device regions that aresingulated in subsequent steps to form a plurality of integrated circuitdies 50.

The substrate 52 has a front surface (e.g., the surface facing upwardsin FIG. 1), sometimes called an active side, and a back surface (e.g.,the surface facing downwards in FIG. 1), sometimes called an inactiveside. The substrate 52 may be a semiconductor, such as silicon, doped orundoped, or an active layer of a semiconductor-on-insulator (SOI)substrate. The substrate 52 may include other semiconductor material,such as germanium; a compound semiconductor including silicon carbide,gallium arsenic, gallium phosphide, indium phosphide, indium arsenide,and/or indium antimonide; an alloy semiconductor including SiGe, GaAsP,AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP; or combinations thereof.Other substrates, such as multi-layered or gradient substrates, may alsobe used.

The devices 54 may be formed in and/or on the front surface of thesubstrate 52. The devices 54 may be transistors, diodes, capacitors,resistors, etc. In embodiments where the integrated circuit dies 50 arelogic dies, the devices 54 include active devices. In embodiments wherethe integrated circuit dies 50 are interposers, the devices 54 may bepassive devices or may be omitted, such that the integrated circuit dies50 are free of active devices. The conductive plugs 56 are electricallyand physically coupled to the devices 54. The ILDs 58 surround thedevices 54 and the conductive plugs 56, and comprise one or moredielectric layers.

The interconnect 60 interconnects the devices 54 to form an integratedcircuit. The interconnect 60 may be formed by, for example,metallization patterns in dielectric layers on the front surface of thesubstrate 52. The metallization patterns include metal lines and viasformed in one or more dielectric layers. The metallization patterns ofthe interconnect 60 are electrically coupled to the devices 54 by theconductive plugs 56.

The die connectors 62 may be conductive pillars (for example, comprisinga metal such as copper, aluminum, tungsten, nickel, or alloys thereof),and are mechanically and electrically coupled to the interconnect 60.The die connectors 62 may be formed by, for example, plating, or thelike. The die connectors 62 electrically couple the respectiveintegrated circuits of the integrated circuit die 50.

The dielectric material 64 is on the active surface of the integratedcircuit dies 50, such as on the interconnect 60. The dielectric material64 laterally encapsulates the die connectors 62, and the dielectricmaterial 64 is laterally coterminous with the integrated circuit die 50.The dielectric material 64 is a silicon containing dielectric layer, andmay be formed of silicon oxide, SiON, SiN, or the like, and may beformed by a deposition process such as CVD, PECVD, PVD, ALD, or thelike. The dielectric material 64 may be a topmost layer of theinterconnect 60.

FIGS. 2A and 2B are cross-sectional views of die stacks 70A and 70B, inaccordance with some embodiments. The die stack 70A and 70B may eachhave a single function (e.g., a logic device, memory die, etc.), or mayhave multiple functions (e.g., a SoC). In a particular embodiment, thedie stack 70A is a processor and the die stack 70B is a memory module.The die stacks 70A and 70B may alternatively be referred to as diestacks 70 here, where references to the die stacks 70 refer to eitherthe die stack 70A or the die stack 70B.

As shown in FIG. 2A, the die stack 70A includes two bonded integratedcircuit dies 50. The die stack 70A may be a processor such as a centralprocessing unit (CPU), graphics processing unit (GPU),application-specific integrated circuit (ASIC), or the like. In aspecific embodiment, the die stack 70A is a GPU. In some embodiments, afirst integrated circuit die 50A and a second integrated circuit die 50Bare bonded such that the active surfaces are facing each other(“face-to-face”). The first and second integrated circuit dies 50 may beconnected by hybrid bonding, fusion bonding, direct bonding, dielectricbonding, metal bonding, or the like. In some embodiments, the firstintegrated circuit die 50A is a processor die, and the second integratedcircuit die 50B is an interface die. The interface die bridges theprocessor die to memory dies, and translates commands between theprocessor and memory dies.

In embodiments where the first and second integrated circuit dies 50 arebonded by hybrid bonding, covalent bonds are formed with oxide layers,such as the dielectric material 64 in each die. Before performing thebonding, a surface treatment may be performed on the first and/or secondintegrated circuit dies 50, forming OH bonds in the top of thedielectric material 64. Next, a pre-bonding process may be performed,where the die connectors 62 and dielectric material 64 of the first andsecond integrated circuit dies 50 are aligned and pressed againsttogether to form weak bonds. After the pre-bonding process, the firstand second integrated circuit dies 50 are annealed to strengthen theweak bonds. During the annealing, OH bonds in the top of the dielectricmaterial 64 break to form Si—O—Si bonds between the first and secondintegrated circuit dies 50, thereby strengthening the bonds. During thehybrid bonding, metal bonding also occurs between the die connectors 62.

Vias 66 may be formed through one of the integrated circuit dies 50 sothat external connections may be made. The vias 66 may be throughsilicon vias (TSVs). In the embodiment shown, the vias 66 are formed inthe second integrated circuit die 50B (e.g., the interface die). Thevias 66 extend through the substrate 52 of the respective integratedcircuit die 50, and may extend through the ILDs 58 to be physically andelectrically connected to the metallization patterns of the interconnect60.

As shown in FIG. 2B, the die stack 70B includes multiple integratedcircuit dies 50 connected by a via 72. The via 72 may be, e.g., a TSV.The die stack 70B may be a memory device such as dynamic random accessmemory (DRAM) dies, static random access memory (SRAM) dies, hybridmemory cube (HMC) modules, high bandwidth memory (HBM) modules, or thelike. In a specific embodiment, the die stack 70B is a HBM module.

Die stacks, such as the die stacks 70, may trap heat, becoming hot spotsin subsequently formed device packages. In particular, die stacksincluding processing devices (such as the die stack 70A) may have a highpower density. For example, in an embodiment where the die stack 70A isa GPU, the power density of the resulting device packages may be fromabout 50 W/cm² to about 300 W/cm². During operation, heat may be trappedat the interface of the processor dies and interface die.

FIGS. 3 through 13 are various views of intermediate steps during aprocess for forming a semiconductor device 300, in accordance with someembodiments. FIGS. 3 through 13 are cross-sectional views. In FIGS. 3through 9, a first device package 100 is formed by bonding variousintegrated circuit dies to a wafer 102. In an embodiment, the firstdevice package 100 is a chip-on-wafer (CoW) package, although it shouldbe appreciated that embodiments may be applied to other 3DIC packages.FIG. 10 shows the resulting first device package 100. In FIGS. 11through 12, a second device package 200 is formed by mounting the firstdevice package 100 to a substrate. In an embodiment, the device package200 is a chip-on-wafer-on-substrate (CoWoS) package, although it shouldbe appreciated that embodiments may be applied to other 3DIC packages.FIG. 13 shows the semiconductor device 300 implementing the resultingsecond device package 200.

The wafer 102 may have a variety of devices formed in it. In particular,interposers, integrated circuit devices, or the like may be formed inthe wafer 102, which may include multiple device regions 100A and 100B(singulated in subsequent steps to form the first device packages 100).

In some embodiments, interposers are formed in the wafer 102. Theinterposers have interconnect structures for electrically connectingactive devices (not shown) in the integrated circuit dies to formfunctional circuits. In such embodiments, the wafer 102 includes asemiconductor substrate having a front surface (e.g., the surface facingupwards in FIG. 3), and a back surface (e.g., the surface facingdownwards in FIG. 3). An interconnect structure is formed on the backsurface of the semiconductor substrate. Through-vias are formed in thesemiconductor substrate extending from the interconnect structure to thefront surface of the semiconductor substrate. Metal lines and vias areformed in an interconnect structure on the semiconductor substrate by,e.g., a dual damascene process. The metal lines and vias may beelectrically connected to the through-vias. The interposers may (or maynot) be free from active devices such as transistors and diodes, and may(or may not) be free from devices such as resistors, inductors,capacitors, and the like.

Although embodiments illustrated herein are discussed in the context ofthe wafer 102 having interposers formed therein, it should beappreciated that other types of devices may be formed in the wafer 102.For example, integrated circuit devices such as logic devices may beformed in the wafer 102. In such embodiments, the wafer 102 includes asemiconductor substrate with active and/or passive devices formedtherein. The semiconductor substrate may be silicon, doped or undoped,or an active layer of a semiconductor-on-insulator (SOI) substrate. Thesemiconductor substrate may include other semiconductor materials, suchas germanium; a compound semiconductor including silicon carbide,gallium arsenic, gallium phosphide, indium phosphide, indium arsenide,and/or indium antimonide; an alloy semiconductor including SiGe, GaAsP,AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP; or combinations thereof.Other substrates, such as multi-layered or gradient substrates, may alsobe used. Devices, such as transistors, diodes, capacitors, resistors,etc., may be formed in and/or on the semiconductor substrate, and may beinterconnected by interconnect structures formed by, for example,metallization patterns in one or more dielectric layers on thesemiconductor substrate to form an integrated circuit.

In FIG. 3, the die stacks 70 are attached to the wafer 102 with dieconnectors 104. In an embodiment, one die stack 70A (e.g., a GPU) andmultiple die stacks 70B (e.g., HBM) may be placed on each device regionof the wafer 102. The die stacks 70 may be attached to the wafer 102using, for example, a pick-and-place tool. The die connectors 104 may beformed from a conductive material such as solder, copper, aluminum,gold, nickel, silver, palladium, tin, the like, or a combinationthereof. In some embodiments, the die connectors 104 are formed byinitially forming a layer of solder through methods such as evaporation,electroplating, printing, solder transfer, ball placement, or the like.Once a layer of solder has been formed on the structure, a reflow may beperformed in order to shape the die connectors 104 into desired bumpshapes. The die connectors 104 form joints between correspondingconnectors on the wafer 102 and the die stacks 70, and electricallyconnect the wafer 102 to the die stacks 70.

In FIG. 4, an underfill 106 may be formed between the die stacks 70 andthe wafer 102, surrounding the die connectors 104. The underfill 106 maybe formed by a capillary flow process after the die stacks 70 areattached, or may be formed by a suitable deposition method before thedie stacks 70 are attached.

In FIG. 5, an encapsulant 108 is formed on the various components. Theencapsulant 108 may be a molding compound, epoxy, or the like, and maybe applied by compression molding, transfer molding, or the like. Theencapsulant 108 may be formed over the wafer 102 such that the diestacks 70 are buried or covered. The encapsulant 108 is then cured.

In FIG. 6, conductive connectors 110 are formed on the back side of thewafer 102. The back side of the wafer 102 may be thinned before theconductive connectors 110 are formed. The thinning may be accomplishedby a chemical-mechanical polish (CMP), a grinding process, or the like.The conductive connectors 110 are electrically connected to features ofthe wafer 102 (e.g., logic devices, interposers, etc.), and may be BGAconnectors, solder balls, metal pillars, controlled collapse chipconnection (C4) bumps, micro bumps, electroless nickel-electrolesspalladium-immersion gold technique (ENEPIG) formed bumps, or the like.In some embodiments, the conductive connectors 110 are formed byinitially forming a layer of solder through such commonly used methodssuch as evaporation, electroplating, printing, solder transfer, ballplacement, or the like. Once a layer of solder has been formed on thestructure, a reflow may be performed in order to shape the material intothe desired bump shapes. After the conductive connectors 110 are formed,the wafer 102 may be placed on tape 112 for subsequent processing steps.

In FIG. 7, the encapsulant 108 is thinned to expose top surfaces of thedie stacks 70. The thinning may be accomplished by a CMP, a grindingprocess, or the like. After the thinning, top surfaces of theencapsulant 108 and die stacks 70 are level.

In FIGS. 8A and 8B, recesses 114 are formed in the die stacks 70. FIG.8A is a cross-sectional view showing processing at the level of thewafer 102, and FIG. 8B is a cross-sectional view showing detailedprocessing at the level of the die stack 70A. The recesses 114 arethrough substrate via (TSV) openings, which are filled later asdiscussed below. The recesses 114 are formed in the substrate 52 of thetopmost die of the die stacks 70. The recesses 114 extend from the backside of the substrates 52, and may be formed so as to extend eithercompletely through or only partially into the substrates 52. In anembodiment, the recesses 114 extend only partially into the substrates52 such that the recesses 114 extend from the back surface of thesubstrates 52 to a depth of less than the total height of the substrates52. Accordingly, while the depth of the recesses 114 is dependent uponthe overall design of the first device packages 100, in some embodimentsthe depth may be from about 50 μm to about 700 μm below the top surfaceof the substrates 52, such as a depth of about 300 μm. Such a depthallows the subsequently formed TSVs to be good conductors of heat forcooling the die stacks 70 while keeping manufacturing costs low.Further, while the width of the recesses 114 is dependent upon theoverall design of the first device packages 100, in some embodiments thewidth may be from about 10 μm to about 200 μm. The recesses 114 may beformed by acceptable photolithography and etching techniques. Forexample, a suitable photoresist may be applied to the wafer 102 (e.g.,on the encapsulant 108 and die stacks 70), and developed. The developedphotoresist may then be used as an etching mask in an etching processfor forming the recesses 114. The etching process may be an anisotropicwet or dry etch.

Once the recesses 114 have been formed, the recesses 114 may be filledwith a liner (not separately illustrated). The liner may be a dielectricmaterial such as silicon nitride, silicon oxide, a dielectric polymer,combinations of these, or the like, and may be formed by a process suchas CVD, oxidation, PVD, ALD, or the like.

The recesses 114 may also be filled with a barrier layer (also notseparately illustrated) over the liner. The barrier layer may be aconductive material such as titanium nitride, although other materials,such as tantalum nitride, titanium, another dielectric, or the like mayalternatively be utilized. The barrier layer may be formed using a CVDprocess, such as PECVD, however, other processes such as sputtering ormetal organic chemical vapor deposition (MOCVD), ALD, or the like mayalternatively be used. The barrier layer may be formed so as to contourto the underlying shape of the recesses 114.

In FIG. 9, a conductive material is formed in the recesses 114, therebyforming dummy TSVs 116. The conductive material may be copper, althoughother suitable materials such as aluminum, tungsten, alloys, dopedpolysilicon, combinations thereof, and the like, may alternatively beutilized. The conductive material may be formed by depositing a seedlayer in the recesses 114 and then electroplating copper onto the seedlayer, filling and overfilling the recesses 114. Once the recesses 114have been filled, excess barrier layer and excess conductive materialoutside of the recesses 114 may be removed through a grinding processsuch as a CMP, although any suitable removal process may be used.

After the conductive material is formed, an annealing process may beperformed. For example, a thermal anneal may be performed at atemperature of about 400° C. for a time span of about 1 hour. The annealmay strengthen the interface of the dummy TSVs 116 and substrates 52,and stabilize the grain structure of the electroplated conductivematerial.

The dummy TSVs 116 are electrically isolated from surrounding devices.Although the dummy TSVs 116 are formed in the substrates 52 of theintegrated circuit dies 50, which themselves may contain devices 54, thedummy TSVs 116 are electrically isolated from the active side of theintegrated circuit dies 50, e.g., from the devices 54 of the integratedcircuit dies 50. For example, the recesses 114 may be formed in thesubstrate 52 of the integrated circuit dies 50 such that the dummy TSVs116 are surrounded by non-conductive materials on all sides except thetop side (e.g., the side of the dummy TSVs 116 level with the back sideof the substrate 52). The non-conductive materials may be insulatingmaterials, bulk semiconductor materials (e.g., a semiconductor materialwith no devices formed therein), or the like. The dummy TSVs 116 may notbe physically or electrically connected to the devices 54, themetallization of the interconnect 60, or the like.

Although the dummy TSVs 116 are only illustrated as being formed in thedie stack 70A, it should be appreciated that the dummy TSVs 116 could beformed in any or all of the die stacks 70. For example, the dummy TSVs116 could be formed in only the die stack 70A, only the die stack 70B,or both the die stacks 70A and 70B.

In FIG. 10, dummy connectors 118 are formed on respective dummy TSVs116. The dummy connectors 118 may be formed on each of the respectivedummy TSVs 116, or on a subset of the dummy TSVs 116 (e.g., the dummyconnectors 118 may only be formed on a subset of the dummy TSVs 116 andmay not be formed on remaining ones of the dummy TSVs 116). Because thedummy connectors 118 are formed on the dummy TSVs 116, they are alsoelectrically isolated from the active side of the substrates 52. Thedummy connectors 118 may be formed from a conductive material such assolder, copper, aluminum, gold, nickel, silver, palladium, tin, thelike, or a combination thereof. In the embodiment shown, the dummyconnectors 118 are bumps formed of a reflowable material, such assolder, smart solder, or the like. The dummy connectors 118 may beformed such that they only cover respective dummy TSVs 116, or may bewider than the dummy TSVs 116 such that they cover respective dummy TSVs116 and extend along top surfaces of the substrate 52 of the topmostintegrated circuit dies 50. The dummy connectors 118 thermally couplethe dummy TSVs 116 to an overlying heat spreader (shown below). Thedummy connectors 118 are sufficiently large so that sufficient heat maybe transferred from the dummy TSVs 116 during operation; in anembodiment, the dummy connectors 118 have a height of from about 25 μmto about 100 μm, such as about 50 μm.

In FIG. 11, the wafer 102 and encapsulant 108 are singulated by asingulation process, thereby forming the first device packages 100. As aresult of the singulation process, the wafer 102 is singulated intointerposers 120, with each of the first device packages 100 having aninterposer 120. The singulation may be performed while the wafer 102 ison the tape 112. Singulation is performed along scribe line regionse.g., between adjacent device regions, e.g., the device regions 100A and100B. In some embodiments, the singulation process includes a sawingprocess, a laser process, or a combination thereof.

FIG. 12 shows a resulting first device package 100 after singulation. Asa result of the singulation process, edges of the interposers 120 andencapsulant 108 are coterminous. In other words, the outer sidewalls ofthe interposers 120 have the same width as the outer sidewalls of theencapsulant 108.

In FIG. 13, the second device package 200 is formed by mounting thefirst device package 100 to a package substrate 202. The packagesubstrate 202 may be made of a semiconductor material such as silicon,germanium, diamond, or the like. Alternatively, compound materials suchas silicon germanium, silicon carbide, gallium arsenic, indium arsenide,indium phosphide, silicon germanium carbide, gallium arsenic phosphide,gallium indium phosphide, combinations of these, and the like, may alsobe used. Additionally, the package substrate 202 may be a SOI substrate.Generally, an SOI substrate includes a layer of a semiconductor materialsuch as epitaxial silicon, germanium, silicon germanium, SOI, SGOI, orcombinations thereof. The package substrate 202 is, in one alternativeembodiment, based on an insulating core such as a fiberglass reinforcedresin core. One example core material is fiberglass resin such as FR4.Alternatives for the core material include bismaleimide-triazine BTresin, or alternatively, other PCB materials or films. Build up filmssuch as ABF or other laminates may be used for package substrate 202.

The package substrate 202 may include active and passive devices (notshown). As one of ordinary skill in the art will recognize, a widevariety of devices such as transistors, capacitors, resistors,combinations of these, and the like may be used to generate thestructural and functional requirements of the design for the seconddevice package 200. The devices may be formed using any suitablemethods.

The package substrate 202 may also include metallization layers and vias(not shown) and bond pads 204 over the metallization layers and vias.The metallization layers may be formed over the active and passivedevices and are designed to connect the various devices to formfunctional circuitry. The metallization layers may be formed ofalternating layers of dielectric (e.g., low-k dielectric material) andconductive material (e.g., copper) with vias interconnecting the layersof conductive material and may be formed through any suitable process(such as deposition, damascene, dual damascene, or the like). In someembodiments, the package substrate 202 is substantially free of activeand passive devices.

In some embodiments, the conductive connectors 110 are reflowed toattach the first device package 100 to the bond pads 204, therebybonding the interposer 120 to the package substrate 202. The conductiveconnectors 110 electrically and/or physically couple the packagesubstrate 202, including metallization layers in the package substrate202, to the second device package 200. In some embodiments, passivedevices (e.g., surface mount devices (SMDs), not illustrated) may beattached to the second device package 200 (e.g., bonded to the bond pads204) prior to mounting on the package substrate 202. In suchembodiments, the passive devices may be bonded to a same surface of thesecond device package 200 as the conductive connectors 110.

The conductive connectors 110 may have an epoxy flux (not shown) formedthereon before they are reflowed with at least some of the epoxy portionof the epoxy flux remaining after the second device package 200 isattached to the package substrate 202. This remaining epoxy portion mayact as an underfill to reduce stress and protect the joints resultingfrom the reflowing the conductive connectors 110.

An underfill 206 may be formed between the first device package 100 andthe package substrate 202, surrounding the conductive connectors 110.The underfill 206 may be formed by a capillary flow process after thefirst device package 100 is attached or may be formed by a suitabledeposition method before the first device package 100 is attached.

In FIG. 14, a heat spreader 208 is attached to the first device package100 and package substrate 202, covering and surrounding the first devicepackage 100. The heat spreader 208 may be formed from a material withhigh thermal conductivity, such as steel, stainless steel, copper, thelike, or combinations thereof. In some embodiments (discussed below),the heat spreader 208 is coated with another metal, such as gold,nickel, or the like. In some embodiments, the heat spreader 208 is asingle contiguous material. In some embodiments, the heat spreader 208includes multiple pieces that may be the same or different materials.

The heat spreader 208 is adhered to the first device package 100 andpackage substrate 202. An adhesive 210 attaches the heat spreader 208 tothe package substrate 202. The adhesive 210 may be epoxy, glue, or thelike, and may be a thermally conductive material. A thermal interfacematerial (TIM) 212 attaches the heat spreader 208 to the first devicepackage 100. The TIM 212 may be a polymeric material, solder paste,indium solder paste, or the like, and may be dispensed on the firstdevice package 100, such as on the die stacks 70, encapsulant 108, anddummy connectors 118. Notably, the TIM 212 surrounds the dummyconnectors 118. The TIM 212 is formed to a thickness sufficiently largeto bury the dummy connectors 118. For example, in embodiments where thedummy connectors 118 are formed to a height of about 50 μm, the TIM 212is formed to a thickness of from about 25 μm to about 200 μm, such asabout 100 μm.

The TIM 212 thermally couples the first device package 100 and heatspreader 208. Because the heat spreader 208 is the primary means of heatdissipation for the first device package 100, the thermal conductivityof the TIM 212 may be a thermal bottleneck for the overall thermalresistance along a thermal path P₁ extending between the heat spreader208 and the bottommost die of the die stacks 70 during operation.Because the dummy connectors 118 are buried in the TIM 212, the thermalresistance along the thermal path P₁ may be decreased. In an embodiment,addition of the dummy connectors 118 may decrease the thermal resistancealong the thermal path P₁ by a factor of ten or more. Further, the dummyTSVs 116 may also decrease the thermal resistance along the thermal pathP₁.

FIG. 15 shows a semiconductor device 300 implementing the resultingsecond device package 200. In the semiconductor device 300, a heatsink302 is adhered to the second device package 200 with a TIM 304. Theheatsink 302 may be formed of a material selected from the candidatematerials for forming the heat spreader 208. The heatsink 302 may beformed of the same material as the heat spreader 208, or may includedifferent materials. The TIM 304 may be similar to the TIM 212, or maybe different. The semiconductor device 300 may be formed in a differentprocess after the process for manufacturing the second device package200. For example, the second device package 200 may be manufactured in afirst process, and the semiconductor device 300 may formed in a secondprocess after manufacture and delivery of the second device package 200.

FIG. 16 shows the semiconductor device 300, in accordance with someother embodiments. In the embodiment shown, the dummy TSVs 116 are notformed such that the die stacks 70 are substantially free of TSVs. Insuch embodiments, the dummy connectors 118 are surrounded bynon-conductive materials on all sides. Although the dummy TSVs 116 maydecrease the thermal resistance along the thermal path P₁, they arecostly to manufacture. Forming the dummy connectors 118 in the TIM 212may sufficiently decrease the thermal resistance along the thermal pathP₁, reducing manufacturing costs by avoiding formation of TSVs.

FIG. 17 shows the semiconductor device 300, in accordance with someother embodiments. In the embodiment shown, the dummy connectors 118 arestuds, pillars, or bumps formed of a conductive material such as copper,aluminum, tungsten, alloys, doped polysilicon, the like, or acombination thereof. In a particular embodiment, the dummy connectors118 are dummy copper pillars. Forming the copper pillars buried in theTIM 212 may decrease the thermal resistance along the thermal path P₁.

The dummy copper pillars may be formed by acceptable photolithographyand plating processes. For example, after dummy TSVs 116 are formed inthe recesses 114 (see, e.g., FIG. 9), a suitable photoresist (not shown)may be applied to the wafer 102 (e.g., on the encapsulant 108 and diestacks 70), and developed. The photoresist may be patterned withopenings exposing the dummy TSVs 116. The openings in the photoresistmay be lined with a barrier layer. The barrier layer may be a conductivematerial such as titanium nitride, tantalum nitride, titanium, anotherdielectric, or the like, and may be formed by CVD, PECVD, MOCVD, ALD, orthe like. The conductive material may then be formed in the openings,thereby forming the dummy connectors 118 (e.g., dummy copper pillars).The conductive material may be formed by depositing a seed layer in theopenings and then electroplating the conductive material onto the seedlayer, filling the openings. The photoresist may then be removed byashing, stripping, or the like.

FIG. 18 shows the semiconductor device 300, in accordance with someother embodiments. In the embodiment shown, an adhesive 122 is formed onthe first device package 100. The adhesive 122 is on the die stacks 70,encapsulant 108, and dummy TSVs 116. The adhesive 122 may be dispensedon the first device package 100 before or after the first device package100 is singulated. The adhesive 122 may be a polymeric material, solderpaste, thermal adhesive, or the like, and may be formed to a thicknessof from about 25 μm to about 150 μm. The dummy connectors 118 are formedon the adhesive 122, and may be formed by a pick and place method. Inthe embodiment shown, the dummy connectors 118 are bumps such as solderballs. In some embodiments, the dummy connectors 118 are not alignedover the dummy TSVs 116. The TIM 212 is dispensed on the adhesive 122and around the dummy connectors 118. The dummy connectors 118 are buriedin the TIM 212. The adhesive 122 may cause the dummy connectors 118 toconform to the shape of the first device package 100, includingconforming to any warpage that may have been introduced in the firstdevice package 100. As such, the overall thermal resistance along thethermal path P₁ may be reduced.

FIG. 19 shows the semiconductor device 300, in accordance with someother embodiments. In the embodiment shown, dummy metallization 124 isformed on the first device packages 100. The dummy metallization 124 maybe formed on the first device package 100 before or after the firstdevice package 100 is singulated. The dummy metallization 124 may beformed from a conductive material or metal such as gold, indium, copper,the like, or combinations thereof. The dummy metallization 124 may beformed by depositing a seed layer over the wafer 102 (e.g., on theencapsulant 108, die stacks 70, and dummy TSVs 116), and thenelectroplating the conductive material onto the seed layer. The dummymetallization 124 may also be formed by sputtering the conductivematerial onto the wafer 102. Like the dummy TSVs 116, the dummymetallization 124 may be electrically isolated from the active and/orpassive devices of the die stacks 70 (e.g., the devices 54) and othersurrounding devices.

The dummy connectors 118 are formed on the dummy metallization 124, andmay be formed by a pick and place method. In the embodiment shown, thedummy connectors 118 are bumps such as solder balls. The TIM 212 isdispensed on the dummy metallization 124 and around the dummy connectors118. The dummy connectors 118 are not buried in the TIM 212. Rather,after formation, the dummy connectors 118 have top surfaces level withor extending above the TIM 212. When the heat spreader 208 is attachedto the first device package 100, the dummy connectors 118 are reflowedto bond the dummy metallization 124 to the heat spreader 208. Solderjoints are thereby formed in the TIM 212 bonding the dummy metallization124 and heat spreader 208. In the embodiment shown, the heat spreader208 is coated with another metal, such as nickel. During reflow, thenickel coating of the heat spreader 208 mingles with the material of theTIM 212 and dummy connectors 118 to form an intermetallic compound (IMC)126 at the interface of the heat spreader 208 and TIM 212. The IMC 126may have different regions; for example, the IMC 126 may have firstregions where a first IMC is formed from the materials of the dummyconnectors 118 and heat spreader 208, and may have second regions wherea second IMC is formed from the materials of the TIM 212 and heatspreader 208. The dummy metallization 124 and IMC 126 may have a highthermal conductivity and may conform to the shape of the first devicepackage 100, including conforming to any warpage that may have beenintroduced in the first device package 100. As such, the overall thermalresistance along the thermal path P₁ may be reduced.

FIG. 20 shows the semiconductor device 300, in accordance with someother embodiments. In the embodiment shown, the dummy connectors 118 arepart of a patterned metal sheet (see, e.g., FIG. 21, which shows atop-down view of the patterned metal sheet). For example, the patternedmetal sheet may be copper foil, such as that used for radio frequencyinterference (RFI) shielding, and may include openings 128. Thepatterned metal sheet may have a thickness of from about 11 μm to about25 μm. The patterned metal sheet is disposed in the TIM 212 such thatthe TIM 212 is disposed between the patterned metal sheet and the firstdevice package 100, and is also disposed between the patterned metalsheet and the heat spreader 208. The patterned metal sheet may have ahigh thermal conductivity and may conform to the shape of the firstdevice package 100, including conforming to any warpage that may havebeen introduced in the first device package 100. As such, the overallthermal resistance along the thermal path P₁ may be reduced.

FIG. 22 shows a flow diagram of a method 400 for manufacturing thesemiconductor device 300, in accordance with some other embodiments. Instep 402, a die stack, such as the die stack 70A, is attached to theinterposer 120. In step 404, the die stack 70A is encapsulated. In step406, the dummy TSVs 116 are optionally formed in the die stack. In step408, the dummy connectors 118 are formed on the die stack. The dummyconnectors 118 may be formed in accordance with any embodiments herein.In step 410, the TIM 212 is dispensed around the dummy connectors 118.In step 412, the heat spreader 208 is attached to the die stack usingthe TIM 212. In subsequent processing steps, the heatsink 302 may beattached to the heat spreader 208.

Embodiments may achieve advantages. The thermal conductivity of the TIM212 may be a significant thermal bottleneck in stacked devices. Formingthe dummy connectors 118 in the TIM 212 and forming the dummy TSVs 116in the die stacks 70 may decrease the thermal resistance along thethermal path P₁. Addition of other features such as the adhesive 122,dummy metallization 124, and eutectic compound 126 may help the TIM 212conform to any warpage that may be introduced in the device package 100.As such, the overall thermal resistance along the thermal path P₁ may bereduced.

In an embodiment, a device includes: a die stack over and electricallyconnected to an interposer, the die stack including a topmost integratedcircuit die including: a substrate having a front side and a back sideopposite the front side, the front side of the substrate including anactive surface; a dummy through substrate via (TSV) extending from theback side of the substrate at least partially into the substrate, thedummy TSV electrically isolated from the active surface; a thermalinterface material over the topmost integrated circuit die; and a dummyconnector in the thermal interface material, the thermal interfacematerial surrounding the dummy connector, the dummy connectorelectrically isolated from the active surface of the topmost integratedcircuit die.

In some embodiments, the dummy connector is a solder connector disposedon the dummy TSV. In some embodiments, the dummy connector is a copperpillar disposed on the dummy TSV. In some embodiments, the devicefurther includes: an adhesive on the topmost integrated circuit die, thedummy connector and the thermal interface material disposed on theadhesive. In some embodiments, the device further includes: dummymetallization on the topmost integrated circuit die, the dummy connectorand the thermal interface material disposed on the dummy metallization,the dummy metallization electrically isolated from the active surface ofthe topmost integrated circuit die; and an eutectic compound on thethermal interface material, the dummy connector bonding the eutecticcompound to the dummy metallization. In some embodiments, the dummyconnector is a patterned metal sheet. In some embodiments, the devicefurther includes: a package substrate, the interposer bonded to thepackage substrate; and a heat spreader adhered to the package substrateand the die stack, the heat spreader covering and surrounding the diestack, the thermal interface material thermally coupling the heatspreader and the die stack. In some embodiments, the die stack furtherincludes: an interface die bonded to the interposer, the topmostintegrated circuit die bonded to the interface die.

In an embodiment, a method includes: attaching a die stack to aninterposer; encapsulating the die stack with an encapsulant; planarizingthe encapsulant, top surfaces of the encapsulant the die stack beinglevel; forming a recess in a topmost integrated circuit die of the diestack, the topmost integrated circuit die including a substrate havingan active surface and a back surface, the substrate having a firstheight, the recess extending a first depth from the back surface of thesubstrate, the first depth less than the first height; filling therecess with a first conductive material to form a dummy throughsubstrate via (TSV); forming a dummy connector on the dummy TSV;dispensing a thermal interface material on the topmost integratedcircuit die, the thermal interface material surrounding the dummyconnector; and attaching a heat spreader to the topmost integratedcircuit die, the heat spreader covering and surrounding the die stackand the interposer.

In some embodiments, the method further includes: forming the interposerin a wafer; and singulating the wafer to form the interposer, theinterposer having the die stack disposed thereon. In some embodiments,the dummy TSV and dummy connector are formed before the singulating thewafer. In some embodiments, the forming the dummy connector on the dummyTSV includes forming solder connectors on the dummy TSV. In someembodiments, the forming the dummy connector on the dummy TSV includes:forming a photoresist on the topmost integrated circuit die; patterningthe photoresist to form an opening exposing the dummy TSV; and forming asecond conductive material in the opening to form the dummy connector.In some embodiments, the method further includes: plating dummymetallization on the topmost integrated circuit die, the thermalinterface material dispensed on the dummy metallization, the dummymetallization electrically isolated from the active surface of thetopmost integrated circuit die. In some embodiments, the dummy connectorincludes a solder connector, the method further including: reflowing thesolder connector to bond the dummy metallization to the heat spreader.In some embodiments, the attaching the die stack to the interposerincludes: bonding the die stack to the interposer with conductiveconnectors; and forming an underfill between the die stack and theinterposer, the underfill surrounding the conductive connectors.

In an embodiment, a method includes: attaching a die stack to aninterposer; encapsulating the die stack with an encapsulant; planarizingthe encapsulant, top surfaces of the encapsulant the die stack beinglevel; dispensing a thermal interface material on the die stack; forminga dummy connector in the thermal interface material, the dummy connectorsurrounded by non-conductive materials on all sides; and attaching aheat spreader to the die stack, the heat spreader covering andsurrounding the die stack and the interposer.

In some embodiments, the forming the dummy connector in the thermalinterface material includes: forming the dummy connector on the diestack. In some embodiments, the forming the dummy connector in thethermal interface material includes: forming dummy metallization on thedie stack; and forming the dummy connector on the dummy metallization.In some embodiments, the forming the dummy connector in the thermalinterface material includes: disposing a patterned metal sheet in thethermal interface material.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: attaching a die stack to aninterposer; encapsulating the die stack with an encapsulant; planarizingthe encapsulant, top surfaces of the encapsulant and the die stack beinglevel after the planarizing the encapsulant; forming a recess in atopmost integrated circuit die of the die stack, the topmost integratedcircuit die comprising a substrate having an active surface and a backsurface, the substrate having a first height, the recess extending afirst depth from the back surface of the substrate, the first depthbeing less than the first height; filling the recess with a firstconductive material to form a dummy through substrate via (TSV); forminga dummy connector on the dummy TSV; dispensing a thermal interfacematerial on the topmost integrated circuit die, the thermal interfacematerial surrounding the dummy connector; and attaching a heat spreaderto the topmost integrated circuit die, the heat spreader covering andsurrounding the die stack and the interposer.
 2. The method of claim 1further comprising: forming the interposer in a wafer; and singulatingthe wafer to form the interposer, the die stack being attached to theinterposer before the singulating the wafer.
 3. The method of claim 2,wherein the dummy TSV and dummy connector are formed before thesingulating the wafer.
 4. The method of claim 1, wherein the forming thedummy connector on the dummy TSV comprises forming solder connectors onthe dummy TSV.
 5. The method of claim 1, wherein the forming the dummyconnector on the dummy TSV comprises: forming a photoresist on thetopmost integrated circuit die; patterning the photoresist to form anopening exposing the dummy TSV; and forming a second conductive materialin the opening to form the dummy connector.
 6. The method of claim 1further comprising: plating dummy metallization on the topmostintegrated circuit die, the thermal interface material being dispensedon the dummy metallization, the dummy metallization being electricallyisolated from the active surface of the topmost integrated circuit die.7. The method of claim 6, wherein the dummy connector comprises a solderconnector, the method further comprising: reflowing the solder connectorto bond the dummy metallization to the heat spreader.
 8. The method ofclaim 1, wherein the attaching the die stack to the interposercomprises: bonding the die stack to the interposer with conductiveconnectors; and forming an underfill between the die stack and theinterposer, the underfill surrounding the conductive connectors.
 9. Amethod comprising: attaching a die stack to an interposer; encapsulatingthe die stack with an encapsulant; planarizing the encapsulant, topsurfaces of the encapsulant and the die stack being level after theplanarizing the encapsulant; dispensing a thermal interface material onthe die stack; forming a dummy connector in the thermal interfacematerial, the dummy connector being surrounded by the thermal interfacematerial on all sides; and attaching a heat spreader to the die stack,the heat spreader covering and surrounding the die stack and theinterposer.
 10. The method of claim 9, wherein the forming the dummyconnector in the thermal interface material comprises: forming the dummyconnector on a topmost integrated circuit die of the die stack.
 11. Themethod of claim 9, wherein the forming the dummy connector in thethermal interface material comprises: forming dummy metallization on atopmost integrated circuit die of the die stack; and forming the dummyconnector on the dummy metallization.
 12. The method of claim 9, whereinthe forming the dummy connector in the thermal interface materialcomprises: disposing a patterned metal sheet in the thermal interfacematerial.
 13. The method of claim 9, wherein a topmost die of the diestack comprises a substrate having an active surface and a back surface,the method further comprising: forming a dummy through substrate via(TSV) in the substrate, the dummy TSV extending partially into thesubstrate from the back surface, the dummy TSV being electricallyisolated from the active surface of the topmost die.
 14. The method ofclaim 13, wherein forming the dummy connector in the thermal interfacematerial comprises forming the dummy connector at an exposed end of thedummy TSV, the dummy connector contacting the back surface of thesubstrate and the exposed end of the dummy TSV.
 15. The method of claim9, wherein the dummy connector has a height of from 25 μm to 100 μm. 16.The method of claim 9, wherein the thermal interface material is apolymeric material.
 17. The method of claim 9, wherein forming the dummyconnector in the thermal interface material comprises: formingreflowable material on a topmost integrated circuit die of the diestack.
 18. The method of claim 9, wherein forming the dummy connector inthe thermal interface material comprises: plating copper pillars on atopmost integrated circuit die of the die stack.
 19. A methodcomprising: attaching a die stack to an interposer, the die stackcomprising active devices, the interposer comprising interconnectstructures, the interconnect structures of the interposer beingelectrically coupled to the active devices of the die stack after theattaching the die stack to the interposer; encapsulating the die stackwith an encapsulant; forming a dummy through substrate via (TSV) in thedie stack; plating dummy metallization on the dummy TSV, the die stack,and the encapsulant; forming a conductive feature on the dummymetallization, wherein the dummy TSV, the dummy metallization, and theconductive feature are electrically isolated from the active devices ofthe die stack and the interconnect structures of the interposer;dispensing a thermal interface material around the conductive featureand on the dummy metallization; and attaching a heat spreader to the diestack with the thermal interface material, the thermal interfacematerial, the dummy metallization, and the conductive feature thermallycoupling the heat spreader to the dummy TSV.
 20. The method of claim 19,wherein the die stack comprises a plurality of substrates, each of thesubstrates having an active surface and a back surface, and whereinforming the dummy TSV comprises: forming the dummy TSV in a topmostsubstrate of the substrates.
 21. The method of claim 20, wherein thedummy TSV extends from the back surface of the topmost substrate to anintermediate point between the back surface and the active surface ofthe topmost substrate.
 22. The method of claim 19, wherein forming theconductive feature comprises: forming a solder connector on the dummymetallization; and reflowing the solder connector, wherein reflowing thesolder connector forms an intermetallic compound at an interface of theheat spreader and the thermal interface material.
 23. The method ofclaim 19, wherein forming the conductive feature comprises: plating acopper pillar on the dummy metallization.